Identification of Sedge Warbler

Sedge WarblerAcrocephalus schoenobaenus

From Wikipedia

The Sedge Warbler (Acrocephalus schoenobaenus) is an Old World warbler in the genus Acrocephalus. It is a medium-sized warbler with a brown, streaked back and wings and a distinct pale supercilium. Sedge Warblers are migratory, crossing the Sahara to get from their European and Asian breeding grounds to spend winter in Africa. The male's song is composed of random chattering phrases and can include mimicry of other species. The Sedge Warbler is mostly insectivorous.

DescriptionThis is a medium-sized warbler, 11.5-13 cm long and weighing around 12 g. It has a streaked brown back and wings, and pale underparts. The rump is warm brown and unstreaked, contrasting with the duller wings. The forehead is flattened, there is a prominent whitish supercilium, the crown is streaked with black, and the bill is strong and pointed. The legs are greyish.

The plumage of the sexes is identical, although they can be told apart when caught for ringing by the presence of a brood patch or cloacal protuberance. Juvenile birds have dark spots on the breast. They can be easier to confuse with Aquatic Warbler Acrocephalus paludicola due to an apparent pale central crown stripe contrasting with the darker edges. Other similar species include Moustached Warbler A. melanopogon and Pallas's Grasshopper-warbler Locustella certhiola. The oldest recorded Sedge Warbler was a bird ringed in Finland which reached the age of 10 years, 1 month. The typical lifespan is 2 years.

TaxonomyThe Sedge Warbler was first described by Carolus Linnaeus in his Systema naturae in 1758 (British ornithologists did not distinguish the species from the Eurasian Reed Warbler until the 18th Century). Its scientific name is derived from the Greek akros, meaning 'pointed', and kephale ('head'), skhoiniklos ('reed') and baino ('to walk'). It is monotypic.

Food and Feeding

Prey taken by Sedge Warblers includes mayflies, dragonflies and damselflies, grasshoppers, bugs, lacewings, moths, beetles and flies. Vegetable material includes elderberries and blackberries. On their wintering grounds food includes non-biting midges and flowers and berries from the Toothbrush Tree Salvadora persica.

In late July, prior to migration, it appears that Sedge Warblers seek out sites with large numbers of Plum-reed Aphids Hyalopterus pruni and stay longer there than at other places; ringing studies show that birds may move considerable distances (eg. from southern England to northern France) in search of food before beginning their actual migration. In Portugal, the aphid supply dries up too early for Sedge Warblers to utilise it, so many birds do not stop off there and are already heavy with fat when they pass through.

Birds with the heaviest fat reserves built up before migration are capable of non-stop flights from Africa to southern Britain, or from Uganda to Iraq, for example. Some double their normal weight when 'fuelling' for migration. Lighter birds are forced to make the journey in several shorter parts.

Sedge Warblers feed in low, thick vegetation, especially reeds and rushes, but also in arable fields and around bushes. A study at Attenborough, Nottinghamshire in England, found that the habitats used for foraging during the breeding season were 47% marshland, mostly Glyceria grasses, 26% shrub, 21% field vegetation and 6% woodland. Feeding techniques include 'picking' insects from vegetation while perched or sometimes hovering, and 'leap-catching', when the bird grabs flying insects as it flies between perches. Sedge Warblers tend to hop between plant stems and pick insects from underneath leaves; they take advantage of the low temperatures around dusk and dawn which make their prey less mobile.